Coding video dissolves using predictive encoders

Abstract

In predictive encoders that support both intra-frame and inter-frame coding, the coding of intermediate dissolve frames (i.e., those falling between the first and last dissolve frames) is restricted, such that either (1) no intermediate dissolve frame is coded as an anchor frame (e.g., MPEG I or P frame) or (2) only a specific number of frames at specific locations within the dissolve are encoded as anchor frames. In certain MPEG implementations, all intermediate dissolve frames are coded as B frames, while the first and last frames are coded as anchor frames (e.g., I or P frames). In other implementations, particular intermediate dissolve frames may be coded as anchor frames with the other intermediate frames coded as B frames. The present invention can provide improved coding results in terms of both bit rate and video quality by avoiding the accumulation of predication errors that can otherwise occur when fixed GOP patterns are applied during dissolves.

What is claimed is:  
     
       1. A method for coding an uncoded video stream using a video compression algorithm that supports both intra-frame coding and inter-frame coding, wherein the video compression algorithm is based on an m-frame GOP pattern having at least one anchor frame per GOP, comprising the steps of: 
       (a) selecting first and last frames corresponding to an n-frame dissolve between a previous scene and a subsequent scene in the uncoded video stream, where n is greater than m; and  
       (b) modifying the m-frame GOP pattern for the n-frame dissolve by constraining the coding of the n frames of the dissolve such that no intermediate frame in the dissolve falling between the first and last frames is coded as an anchor frame.  
     
     
       2. The invention of  claim 1 , wherein all intermediate frames in the dissolve are coded as B frames. 
     
     
       3. The invention of  claim 1 , wherein the first and last frames of the dissolve are coded as anchor frames. 
     
     
       4. The invention of  claim 3 , wherein the last frame of the dissolve is coded as an intra-encoded frame. 
     
     
       5. A machine-readable medium, having encoded thereon program code, wherein, when the program code is executed by a machine, the machine implements a method for coding an uncoded video stream using a video compression algorithm that supports both intra-frame coding and inter-frame coding, wherein the video compression algorithm is based on an m-frame GOP pattern having at least one anchor frame per GOP, comprising the steps of: 
       (a) selecting first and last frames corresponding to an n-frame dissolve between a previous scene and a subsequent scene in the uncoded video stream, where n is greater than m; and  
       (b) modifying the m-frame GOP pattern for the n-frame dissolve by constraining the coding of the n frames of the dissolve such that no intermediate frame in the dissolve falling between the first and last frames is coded as an anchor frame.  
     
     
       6. The invention of  claim 5  wherein all intermediate frames in the dissolve are coded as B frames. 
     
     
       7. The invention of  claim 5 , wherein the first and last frames of the dissolve are coded as anchor frames. 
     
     
       8. The invention of  claim 7 , wherein the last frame of the dissolve is coded as an intra-encoded frame. 
     
     
       9. A method for coding a video stream using a video compression algorithm that supports both intra-frame coding and inter-frame coding, comprising the steps of: 
       (a) selecting first and last frames corresponding to an n-frame dissolve between a previous scene and a subsequent scene in the video stream; and  
       (b) constraining the coding of the n frames of the dissolve such that only two or more intermediate frames at two or more specific locations within the dissolve are coded as anchor frames, where the two or more specific locations are functions of the number n of frames in the dissolve and all other intermediate frames are coded as non-anchor frames, wherein:  
       a first intermediate frame corresponding to a first specified dissolve weighting factor k is coded as a first additional anchor frame inserted into the dissolve; and  
       a second intermediate frame corresponding to a second specified dissolve weighting factor k is coded as a second additional anchor frame inserted into the dissolve.  
     
     
       10. The invention of  claim 9 , wherein: 
       the first dissolve weighting factor k is approximately 0.25; and  
       the second dissolve weighting factor k is approximately 0.75.  
     
     
       11. The invention of  claim 9 , wherein one or more additional intermediate frames corresponding to one or more additional specified dissolve weighting factors k are coded as one or more additional anchor frames inserted into the dissolve. 
     
     
       12. The invention of  claim 9 , wherein the video compression algorithm is based on an m-frame GOP pattern, where n is greater than m. 
     
     
       13. The invention of  claim 9 , wherein the first and last frames of the dissolve are coded as anchor frames. 
     
     
       14. The invention of  claim 13 , wherein the last frame of the dissolve is coded as an intra-encoded frame. 
     
     
       15. A machine-readable medium, having encoded thereon program code, wherein, when the program code is executed by a machine, the machine implements a method for coding a video stream using a video compression algorithm that supports both intra-frame coding and inter-frame coding, comprising the steps of: 
       (a) selecting first and last frames corresponding to an n-frame dissolve between a previous scene and a subsequent scene in the video stream; and  
       (b) constraining the coding of the n frames of the dissolve such that only two or more intermediate frames at two or more specific locations within the dissolve are coded as anchor frames, where the two or more specific locations are functions of the number n of frames in the dissolve and all other intermediate frames are coded as non-anchor frames, wherein:  
       a first intermediate frame corresponding to a first specified dissolve weighting factor k is coded as a first additional anchor frame inserted into the dissolve; and  
       a second intermediate frame corresponding to a second specified dissolve weighting factor k is coded as a second additional anchor frame inserted into the dissolve.  
     
     
       16. A method for coding an uncoded video stream using a video compression algorithm that supports both intra-frame coding and inter-frame coding, wherein the video compression algorithm is based on an m-frame GOP pattern having at least one anchor frame per GOP, comprising the steps of: 
       (a) selecting first and last frames corresponding to an n-frame dissolve between a previous scene and a subsequent scene in the uncoded video stream, where n is greater than m; and  
       (b) modifying the m-frame GOP pattern for the n-frame dissolve by constraining the coding of the n frames of the dissolve such that either (1) no intermediate frame in the dissolve falling between the first and last frames is coded as an anchor frame or (2) only one or more intermediate frames at one or more specific locations within the dissolve are coded as anchor frames, where the one or more specific locations are functions of the number n of frames in the dissolve and all other intermediate frames are coded as non-anchor frames, the all other intermediate frames corresponding to one or more intermediate frames, wherein the first and last frames of the dissolve are coded as anchor frames.  
     
     
       17. The invention of  claim 16 , wherein the last frame of the dissolve is coded as an intra-encoded frame. 
     
     
       18. A method for coding an uncoded video stream using a video compression algorithm that supports both intra-frame coding and inter-frame coding, wherein the video compression algorithm is based on an m-frame GOP pattern having at least one anchor frame per GOP, comprising the steps of: 
       (a) selecting first and last frames corresponding to an n-frame dissolve between a previous scene and a subsequent scene in the uncoded video stream, where n is greater than m; and  
       (b) modifying the m-frame GOP pattern for the n-frame dissolve to constrain the coding of the n frames of the dissolve such that only one or more intermediate frames at one or more specific locations within the dissolve are coded as anchor frames, where the one or more specific locations are functions of the number n of frames in the dissolve and all other intermediate frames are coded as non-anchor frames, the all other intermediate frames corresponding to one or more intermediate frames, wherein modifying the m-frame GOP pattern comprises at least one of:  
       (1) changing the number of frames in the GOP pattern;  
       (2) changing at least one anchor frame in the GOP pattern into a non-anchor frame; and  
       (3) changing at least one non-anchor frame in the GOP pattern into an anchor frame.  
     
     
       19. The invention of  claim 18 , wherein: 
       an intermediate frame corresponding to a dissolve weighting factor k of approximately 0.25 is coded as a first additional anchor frame inserted into the dissolve; and  
       an intermediate frame corresponding to a dissolve weighting factor k of approximately 0.75 is coded as a second additional anchor frame inserted into the dissolve.  
     
     
       20. The invention of  claim 18 , wherein the first and last frames of the dissolve are coded as anchor frames. 
     
     
       21. The invention of  claim 20 , wherein the last frame of the dissolve is coded as an intra-encoded frame. 
     
     
       22. The invention of  claim 18 , wherein modifying the m-frame GOP pattern comprises changing the number of frames in the GOP pattern. 
     
     
       23. The invention of  claim 18 , wherein modifying the m-frame GOP pattern comprises changing at least one anchor frame in the GOP pattern into a non-anchor frame. 
     
     
       24. The invention of  claim 18 , wherein modifying the m-frame GOP pattern comprises changing at least one non-anchor frame in the GOP pattern into an anchor frame. 
     
     
       25. The invention of  claim 18 , wherein n is greater than m+1 and no intermediate frame in the dissolve is coded as an I frame. 
     
     
       26. The invention of  claim 18 , wherein modifying the m-frame GOP pattern further comprises selecting the one or more specific locations based on the number n of frames in the dissolve.